Psuedo-diphtheritic Tracheitis in Broilers

Dr. Jim Hanson

Pseudodiphtheria is a form of diphtheria in which there is development of a false membrane not due to Coynebacterium diphtheriae.

I used the term for development of a ring of necrotic debris, inflammatory cells, sloughed epithelium and fibrin, lining the lumen of the trachea. In a space of 11 days I saw submissions of birds with this lesion from six different farms. The usual history included extremely high mortality. Birds originated from different hatcheries and two flocks were in the Calgary area, four in the Edmonton area.

Three cases involved the same hatchery and occurred over a space of four days. One producer reported a loss of 1000 chicks out of 25,000 by the second day of placement. A second producer was losing between 400 and 500 chicks per day after three days, from a flock of 28,000. The third indicated losses of 150 to 300 per day from 49,000. The tracheal lesions in the chicks were evident grossly and were quite remarkable. The presence of a yellow pseudo-membrane on the mucosa could be seen even without opening the trachea. The lesions were generally confined to the trachea in the first case. In the other two, septicemia with visceral organ involvement was equally prominent.

Microscopic examination revealed a hyper-plastic tracheal epithelium, which was sloughing in places. Mucous glands and goblet cells were dilated. There was a ring of necrotic debris, inflammatory cells, bacterial colonies, plant material and fibrin encircling the lumen.

A fourth submission from the Edmonton area involved older birds. These were three-week-old broilers. The producer indicated seeing no symptoms, just heavy mortality. He had been losing about 60 birds per day out of 19,000 for the last four days. On post mortem examination, two of the birds had caseous debris attached to the distal tracheal mucosa and bronchi. The date of this submission was the same as that of two of the cases mentioned earlier.

One submission from the Calgary area was made during the same four day period. Again, the producer described “no symptoms, just heavy mortality”. On the post mortem examination, of these 30-day-old broilers, similar rings of necrotic material were seen in several tracheae. Microscopically, bacterial colonies were very evident and were seen to be invading sub-epithelial blood vessels. The epithelium was sloughing and there was some blood in the inflammatory debris. No intra-nuclear inclusions were found and an F.A.T. for Laryngotracheitis was negative.

The final submission was actually two broiler breeder birds. This owner reported a loss of 50 birds out of a flock of 15,000 over a one-week period. Egg production dropped by 2 to 3 percent over the week, and then recovered. Mortality also returned to normal after one week. An E. coli septicemia was present, along with a prominent tracheitis. Histologically, numerous bacteria were present in the necrotic debris that ringed the tracheal lumen. No inclusions were seen, but bacteria invading blood vessels were noted.

I spent a weekend mulling over this potential serious disease causing huge losses on these farms. My mind wandered to exotic viruses, new pathogenic bacteria, unknown agents. Then Monday I began to get more information from farm sources along with lab results.

“Common conditions occur most commonly”

The first three cases came from the same hatchery. They had phoned and described a peculiar pocket of air arising from the lower, lateral side of the neck in some of their chicks at time of hatch. This was air within the crop. The chicks had obviously been gulping air. On examination of equipment, formaldehyde was found to be dripping from the nozzles when the second hatch was pulled. I think the exposure to the gas resulted in the tracheitis. Perhaps loss of ciliary action allowed bacteria to enter and proliferate. I didn’t appreciate eye lesions and the chick down did not seem to be off color.

The three-week-old broilers from Edmonton area had numerous mycotic elements associated with the lesion. From the morphology of the hyphae these most likely were aspergillus. Topping up the bedding with moldy straw is the most probable exposure.

We did not find inclusions in the tracheas of the broiler breeders; however, there was a strong positive fluorescence to laryngotracheitis on the F.A.T.

I never did get an answer to the last case. This farm has multiple ages of birds, and routinely vaccinates for bronchitis and Newcastle. Perhaps the tracheitis could be associated with a harsh vaccination reaction occurring in these birds. This would suppose the birds were not vaccinated, or did not respond to a vaccine when given earlier, and responded more harshly when exposure occurred later. Secondary bacterial infections were causing the high mortality.

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Last modified: 5/28/2009